Ticks and mites are both members of the taxonomic order Acari, within the Class Arachnida, and they are collectively referred to as acarines. They are not related to insects. Numerous acarine species are key pests of wildlife, farm and companion animals, humans, and crops.
Ticks are obligate ectoparasites that infest mammals, birds, reptiles, and amphibians. It has been estimated that about 80% of the world's cattle are infested with ticks, causing economic losses of US $7.5 billion. Many tick species are considered a problem primarily because of their ability to transmit numerous pathogens of significant veterinary and human public health importance. Selected examples of the many tick species of importance for pathogen transmission include, but are not limited to, the dog tick Rhipicephalus sanguineus, the lone star tick Amblyomma americanum, the bont tick Amblyomma hebraeum, the tropical bont tick Amblyomma variegatum, the winter tick Dermacentor albipictus, the tropical horse tick Dermacentor nitens, the American dog tick Dermacentor variabilis, the Rocky Mountain wood tick Dermacentor Andersoni, the cattle ticks Boophilus microplus and Boophilus annulatus, Ixodes ricinus, and the deer tick Ixodes scapularis. The bacterial (including rickettsial), protozoan, and arboviral pathogens transmitted by ticks are responsible for a wide variety of human and animal diseases including, for example, Lyme disease, tularemia, heartwater (cowdriosis), dermatophilosis, anaplasmosis, theileriosis, encephalitis, babesiosis, and various spotted fever group rickettsial diseases, including Rocky Mountain spotted fever. For some ticks, however, the major concern is not pathogen transmission, but rather secretion of paralytic neurotoxins that can sometimes be fatal to animals and humans; ticks in this category include, but are not limited to, the Australian paralysis tick Ixodes holocyclus and the African paralysis tick Ixodes rubicundis. Ticks also cause significant losses in the livestock industry due to lesions from bites and occurrence of secondary infections.
There are about 7,000 species of plant-feeding (phytophagous) mites, many of which are pests of timber, fruits, vegetables, forest crops, ornamental plants, and stored grains. The majority of these mites belong to the superfamilies Eriophyoidea (gall, erinose, bud, and rust mites) and the agronomically important Tetranychoidea (spider mites and flat mites). In addition, some mites are endo- or ectoparasitic pests of livestock and companion animals, causing diseases such as mange and scabies, while dust mites produce allergens associated with asthma and other allergic conditions in humans. Mites often rapidly acquire resistance to miticidal agents because of their extremely rapid life cycle (e.g., 1-4 weeks) and ability to deposit large numbers of eggs. Some mites are resistant to virtually all extant pesticidal agents.
Mites and ticks are acarines and are not closely related to insects. Consequently most insecticides are not effective against acarines. Chemicals that are effective against acarines are called acaricides. There are at least two major problems with the few available acaricides that are effective against mites and ticks. First, many species of ticks and mites have developed resistance to various classes of these chemicals. There is already widespread resistance to coumaphos and the pyrethroids, and increasing reports of resistance to amitraz. The macrocyclic lactone endectocides are effective against Boophilus but not against multi-host ticks. Second, many acaricides are under intense regulatory scrutiny by the U.S. Environmental Protection Agency and some have already been deregistered (e.g., chlorpyrifos and diazinon). The loss of major classes of acaricides due to resistance development or deregistration, combined with more demanding registration requirements for new acaricides, is likely to decrease the pool of effective chemical acaricides in the near future. Thus, there is an urgent need to isolate new and safe acaricidal compounds.
A number of investigators have recognized spider venoms as a possible source of insect toxins. A class of peptide toxins known as the omega-atracotoxins, disclosed in U.S. Pat. No. 5,763,568, were isolated from Australian funnel-web spiders by screening the venom for “anti-cotton bollworm” activity. One of these compounds, designated omega-ACTX-Hv1a, has been shown to selectively inhibit insect, as opposed to mammalian, voltage-gated calcium channel currents. A second, unrelated family of insect-specific peptidic calcium channel blockers are disclosed as being isolated from the same family of spiders in U.S. Pat. No. 6,583,264. There is, however, no suggestion in either of these references that such peptides are useful in killing pests other than insects.